ILC7280CS-3028 查看數據表（PDF） - Impala Linear Corporation

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ILC7280CS-3028

Micropower Dual 150mA CMOS RF LDO™ Regulators with 75dB Ripple Rejection

Impala Linear Corporation 

Micropower Dual 150mA CMOS RF LDO™ Regulators with 75dB Ripple Rejection

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APPLICATIONS INFORMATION

+VIN A and B

These pins are connected internally through a galvanic

connection for maximum power from each regulator, both

VINA and VINB must be connected externally to VDD.

Enable/Shutdown

Forcing ENA and/or ENB to a voltage greater than 2V,

enables the regulator(s). These inputs are CMOS logic

compatible gates. If this feature is not required, connect

ENA and/or ENB to VIN. Note that VINA and VINB are con-

nected internally. To minimize the effect of imbalanced

current sharing and possible noise, both VINA and VINB

should also be connected externally.

Input Capacitor

A 1µF capacitor should be placed from VINA/B to GND if

there is more than 10 inches of wire between the input and

the ac filter capacitor or if a battery is used as the input.

Reference Bypass Capacitor

CNOISE (the reference voltage bypass capacitor) is con-

nected to the internal Vref which is common to regulator's

A and B. A 22pF capacitor connected between CNOISE and

GND decouples the reference output voltage and provides

a significant reduction in regulator output noise. An effect

of CNOISE also reduces the regulator phase margin. When

using CNOISE, output capacitors of 2.2µF or greater are

required to maintain stability.

Also affected by CNOISE is the start up speed of the ICL7280.

The speed is inversely proportional to the value of CNOISE. If

a slow or delayed start up time is desired, a larger value of

CNOISE is used. Conversely, faster start up times or instant-on

applications will require smaller values of CNOISE or its omis-

sion with the pin left open. The trade-off of noise to response

should be considered.

Output Capacitor

An output capacitor is required from VOUTA and VOUTB to

GND to prevent oscillation and minimize the effect of load

transient currents. The minimum size of the output capac-

itor(s) is dependent on the usage of CNOISE and its value.

Without CNOISE, a minimum of 1µF is recommended. For

CNOISE = 22pF, a minimum of 2.2µF is recommended

(See figure 1). Larger values of output capacitance will

slow the regulator's response during power up. The upper

limit of capacitance is indefinite, however, it should have

an equivalent series resistance (ESR) of approximately

5Ω or less and a series resonance above 1MHz. Stability

is assured with the use of a capacitor having ultra-low

ESR and as such will not produce low amplitude oscilla-

tions nor an underdamped transient response. This

allows the use of modern ceramic capacitors in prefer-

ence to their more costly Tantalum counterparts.

If the system design calls for smaller load currents, lower

capacitance may be used. Below 10mA the capacitance

may be reduced to 0.47µF and below 1mA to 0.33µF.

No-Load Stability

The ILC7280 will remain stable and in regulation with no

load current. These are desirable performance features

for applications such as keep-alive modes in CMOS sys-

tems.

Split-Supply Operation

When using the ILC7280 in a system requiring that the

load be returned to the negative voltage source, the out-

put(s) must be diode clamped to inhibit significant volt-

age excursions below ground. A simple external diode

clamp to ground will afford protection from damage to

the device. (See figure below).

+VIN

ENA/ENB

ILC7280

Dual Regulator

VOUTA or VOUTB

Dext

Rload

-VIN

External Diode, Dext inhibits significant voltage excursions

below ground in a split power supply load return.

Impala Linear Corporation

ILC7280 1.8

(408) 574-3939 www.impalalinear.com

May 2000 7

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